A new study by a coalition of gun-control groups, including Mayors Against Illegal Guns, found that in states that have implemented "stand your ground" laws, the number of justifiable homicides has skyrocketed.

The rate is up 53 percent in 22 states, according to the study. In Florida, the average annual rate is up 200 percent. In states that do not have those laws, the rate has declined marginally.

The study, co-sponsored by the National Urban League and VoteVets.org, also concludes that the number of deaths of black people deemed to be justifiable in states with those laws has doubled.

"These laws can have deadly consequences, particularly for African-Americans," former New Orleans Mayor Marc Morial, president of the National Urban League, said in a prepared statement. "We need our elected officials to reform these policies to make sure we're doing the right things to reduce unjustified shootings and save lives."

The 28-page report was released one day before a congressional hearing on the issue, scheduled by the Senate Judiciary Subcommittee on the Constitution, Civil Rights and Human Rights.

Marion Hammer, chief lobbyist for the NRA in Florida, and Sean Caranna of Florida Carry, two gun-rights groups, did not return phone calls seeking comment Monday.

The report cites a variety of sources, but principally data from the FBI, which categorizes justifiable homicides as "the killing of a felon during the commission of a felony by a private citizen."

Florida's "stand your ground" law and comparable laws in 21 other states have come in for harsh criticism since Neighborhood Watch volunteer George Zimmerman killed Trayvon Martin, an unarmed black teenager, in Sanford on Feb. 26, 2012.

Zimmerman says he acted in self-defense and pulled his 9mm handgun only after Trayvon attacked him, pinning him to the ground and banging his head against a sidewalk.

Florida's "stand your ground" law, implemented in 2005, allows someone with a reasonable fear of imminent death or great bodily injury to use deadly force.

A six-member Seminole County jury acquitted Zimmerman on July 13 after listening to four weeks of evidence and the judge's instructions on the law, which included a primer on justifiable homicide.

Trayvon's parents have vowed to work to repeal "stand your ground" in Florida and similar laws in other states.

It's not clear what success they will have. In Florida, the law is popular with residents and legislators. A blue-ribbon panel, appointed by Gov. Rick Scott, conducted a series of public hearings last year and, in the end, recommended no changes.

But Zimmerman's acquittal set off civil-rights rallies across the country, including violent ones in Los Angeles and Oakland, Calif., and activists in Tallahassee had a 31-day sit-in outside the governor's office. Among that group's demands: that "stand your ground" be reviewed or reworked.

A poll of Florida legislators, however, showed that by a margin of 108-47, lawmakers opposed calling a special session to do that.

Still, the Florida House Subcommittee on Criminal Justice, headed by Matt Gaetz, R-Fort Walton Beach, has been ordered to conduct a public hearing before the start of the next session.

Gaetz was quoted as saying his plans were to change not a single "comma."

The three groups behind the study have been vocal in their opposition to such laws, calling them "shoot first" laws and saying they have made cities more dangerous.

"There is significant evidence that Stand Your Ground laws undermine public safety," according to the study's authors, who compared justifiable-homicide numbers between 2005 and 2011.